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FILE – This Thursday, September 7, 2017, a satellite image made available by NOAA shows the eye of Hurricane Irma, left north of the island of Hispaniola, with Hurricane Jose, right, in the 'Atlantic Ocean. Six major hurricanes – with winds of at least 111 km / h (178 km / h) revolved around the Atlantic in 2017, including Harvey, Irma and Maria, who hit parts of the US United and Caribbean. (NOAA via AP) (Associated Press)
WASHINGTON – The warmer waters of the Atlantic last year caused an unusual number of major hurricanes.
Last year, six major hurricanes, with winds of at least 111 km / h (178 km / h), revolved around the Atlantic, including Harvey, Irma and Maria, who hit areas of the United States and the Caribbean. Since 2000, the Atlantic has averaged three major hurricanes a year. Before that, the average was closer to two.
According to a study published Thursday in the journal Science, there could be five to eight major hurricanes per year around 2100.
"We will witness more active hurricane seasons like 2017 in the future," said lead author, Hiro Murakami, a climatologist and hurricane specialist at the National Oceanic and Atmospheric Administration.
So far this year, only an Atlantic hurricane, Florence, has reached a major status.
Hot water serves as fuel for hurricanes. The water must be at least 79 degrees (26 degrees Celsius) for a storm to form. The hotter the water, the more it can withstand the forces that would weaken it, said Brian McNoldy, hurricane researcher at the University of Miami.
Murakami found that a combination of natural conditions and human-caused climate changes made the waters warmer in a key area, which caused more major storms. This area is essentially a large box located south of Florida and north of South America, which extends east to Africa.
Some of the most powerful hurricanes in the Atlantic form off the west coast of Africa, then head to the Caribbean and the east coast of the United States.
The water in this big box – the main hurricane development region – averaged 0.7 degrees (0.4 degrees Celsius) warmer than normal for the entire 2017 season, which is unusual for a six months, said Murakami.
The Murakami study used computer simulations to isolate different climatic conditions. Although his research showed both natural and man-made causes from the burning of coal, oil and gas, Murakami said he could not separate them enough to see which was the biggest .
He used computer models to project himself into the future. The Atlantic should warm up faster than the rest of the world's oceans. This difference is why Murakami said that the number of major storms would probably increase by two or more on average.
Some outside experts have had problems with some parts of the Murakami study.
McNoldy said it was logical that unusual hot water was involved in 2017, but he was not quite ready to point fingers at global warming.
"The hurricane seasons do not stop being more active as the climate warms. The variability is huge, "said McNoldy in an email.
Kevin Trenberth of the National Center for Atmospheric Research criticized Murakami's study for not taking into account the strong increase in ocean heat in deeper areas, which is also due to climate change.
Gabriel Vecchi of Princeton University said some computer simulations did not show the fastest warming in the Atlantic.
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Follow Seth Borenstein on Twitter: @borenbears. His work can be found here.
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